The present invention relates to a disc brake suitable for use in an automotive vehicle and operable to apply a braking force thereto.
A known disc brake typically comprises an anchor or carrier including a pair of axial arms spaced along the circumference of and extending over the outer periphery of a disc and having respective disc-passing regions, a caliper slidably supported on the arms and configured to straddle the disc between the arms, a pair of inboard and outboard friction pads urged into frictional engagement with opposite sides of the disc when a piston is moved in the cylinder of the caliper, and a pair of return springs adapted to constantly urge the inboard and outboard friction pads in directions away from the disc.
When the brake is actuated, hydraulic fluid is forced into the cylinder of the caliper to cause the piston to move toward the disc. Also, the entire caliper is inwardly slid or displaced relative to the carrier. The outer leg of the caliper and the piston then coact to urge the inboard and outboard friction pads into frictional engagement with opposite sides of the disc so as to apply a braking force thereto.
When the brake is released to stop feeding of the hydraulic fluid, the piston is moved back into the cylinder. At this time, the inboard and outboard return springs act to urge the inboard and outboard friction pads in directions away from the disc.
Typically, a piston seal is disposed between the cylinder and the piston and made of rubber or similar material. When the brake is released, the piston is returned to the cylinder due to springback of the piston seal. As such, the inboard return springs are free to urge the inboard friction pad in a direction away from the disc without receiving a substantial amount of resistance from the piston. The outboard return springs in turn urge the outboard friction pad in a direction away from the disc while the entire caliper is outwardly moved relative to the piston under the influence of the piston seal.
As previously mentioned, the piston is moved back into the cylinder under the influence of the piston seal when the brake is released. During this movement, the inboard friction pad is moved relative to the caliper. That is, the inboard friction pad is moved toward the inboard leg of the caliper under the action of the inboard return springs without receiving a substantial amount of resistance from the piston. Thus, the inboard friction pad can readily be separated from the disc.
The outboard friction pad is, in turn, urged against the outboard leg of the caliper merely under the action of the outboard return springs. Therefore, the outboard friction pad can not be separated from the disc during movement of the piston unless the entire caliper is outwardly moved relative to the carrier.
Where the entire caliper is not sufficiently outwardly moved relative to the carrier, the outboard friction pad remains in sliding contact with the disc. This results in what is referred to in the art as "drag" of the brake. Such drag brings about a deterioration in fuel economy and leads to immature wear of the friction pad.
To safely separate the outboard friction pad from the disc, attempts may be made to change the shape of the outboard return springs so that the amount of a force applied from the outboard return springs to the outboard friction pad is greater than the amount of a force applied from the inboard return springs to the inboard friction pad. However, this change in shape results in an increase in the number of required parts and the number of steps of mounting the return springs during assembly and also, makes it difficult to properly mount the inboard and outboard return springs.
In view of the foregoing, it is an object of the present invention to provide a disc brake which enables ready separation of both inboard and outboard friction pads from a disc, which effectively prevents the occurrence of "drag", and which allows for the use of identical inboard and outboard return springs and thus facilitates mounting of the return springs.